1. Field of the Invention
The present invention relates to an electronic distance meter having a sighting telescope.
2. Description of the Related Art
When a surveyor measures the distance between two points, an electronic distance meter (EDM) is generally used. An electronic distance meter calculates the distance via the phase difference between a projecting light (external light) and a reflected light and via the initial phase of an internal reference light, or via the time difference between the projecting light and the reflected light.
A typical electronic distance meter is provided, behind the objective lens of a sighting telescope thereof, with a light transmitting mirror (reflection member) positioned on the optical axis of the sighting telescope to project the measuring light (externally-projecting light) toward a target (sighting object) through the center of the entrance pupil of the objective lens of the sighting telescope. The light which is reflected by the target to be passed through the objective lens of the sighting telescope passes the peripheral space of the light transmitting mirror to be captured via a wavelength selection filter and a light receiving mirror.
In such an electronic distance meter, the light which is reflected by the target to be passed through the objective lens of the sighting telescope is interrupted by the aforementioned light transmitting mirror by a greater amount as the target is closer to the electronic distance meter. If the light which is reflected by the target to be passed through the objective lens of the sighting telescope is interrupted by the light transmitting mirror by a great amount, the light amount of the incident light upon the aforementioned light receiving mirror decreases, which deteriorates the precision in measuring the object distance. If the target is very close to the electronic distance meter, the light which is reflected by the target to be passed through the objective lens of the sighting telescope may not be incident on a light receiving element (photo-receiver) at all, which makes it impossible to perform a distance measuring operation. To prevent these problems from occurring, various methods have been proposed.
The present invention has been devised in view of the problems noted above, and accordingly, an object of the present invention is to provide an electronic distance meter which is free from the aforementioned problems without deteriorating the performance characteristics of the distance measuring operation of the electronic distance meter with a complicated system.
Another object of the present invention is to provide an electronic distance meter equipped with an autofocus system which is free from the aforementioned problems without deteriorating the performance characteristics of the distance measuring operation of the electronic distance meter with a complicated system.
To achieve the objects mentioned above, according to an aspect of the present invention, an electronic distance meter including a sighting telescope having an objective lens for sighting an object; a reflection member positioned behind the objective lens; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light via the reflection member and the objective lens, and a light-receiving optical system for receiving light which is reflected by the object, subsequently passed through the objective lens and not interrupted by the reflection member; a beam-diameter varying device, provided in association with the light-transmitting optical system, for varying a beam diameter of the measuring light; and a controller which varies the beam diameter via the beam-diameter varying device in accordance with a distance from the object to the electronic distance meter.
Preferably, the controller controls the beam-diameter varying device to increase the beam diameter when the object is in a predetermined short distance range.
In an embodiment, the electronic distance meter further includes a light-emitting element which emits the measuring light; wherein the beam-diameter varying device includes a lens, the beam-diameter varying device inserting and retracting the lens into and from an optical path of the light-transmitting optical system in front of the light-emitting element in accordance with the distance.
In an embodiment the lens is a negative lens, the beam-diameter varying device inserting the negative lens into the optical path when the object is in a predetermined shorter distance range, the beam-diameter varying device retracting the negative lens from the optical path when the object is in a predetermined longer distance range.
In an embodiment, the lens is a positive lens, the beam-diameter varying device inserting the positive lens into the optical path when the object is in a predetermined longer distance range, the beam-diameter varying device retracting the positive lens from the optical path when the object is in a predetermined shorter distance range.
In an embodiment, the electronic distance, meter further includes a light-emitting element which emits the measuring light, wherein the beam-diameter varying device includes a moving device for moving the light-emitting element in a direction of an optical axis of the light-transmitting optical system.
Preferably, the electronic distance meter further includes a lens position detection device which detects an axial position of a focusing lens of the sighting telescope which is moved in an optical axis thereof to bring the object into focus; wherein the beam-diameter varying device is operated in accordance with the axial position of the focusing lens that is detected by the lens position detection device.
Preferably, the reflection member is made of a parallel-plate mirror having front and rear surfaces parallel to each other, wherein the front surface faces the objective lens and is formed as a light transmitting mirror.
In an embodiment, the light-transmitting optical system includes a collimating lens positioned in front of the light-emitting element, the beam-diameter varying device inserting and retracting the lens into and from the optical path of the light-transmitting optical system in front of the collimating lens in accordance with the distance.
In an embodiment, the light-receiving optical system includes a wavelength selection filter positioned between the objective lens and the focusing lens.
In an embodiment, the beam-diameter varying device includes a motor for moving the lens.
According to another aspect of the present invention, an electronic distance meter equipped with an autofocus system is provided, including a sighting telescope for sighting an object, the telescope including an objective lens and a focusing lens; a reflection member positioned behind the objective lens; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light via the reflection member and the objective lens, and a light-receiving optical system for receiving light which is reflected by the object, subsequently passed through the objective lens and eventually not interrupted by the reflection member; a beam-diameter varying device, provided in association with the light-transmitting optical system, for varying a beam diameter of the measuring light; a focus detecting device for detecting a focus state of the sighting telescope; an autofocus drive system which drives the focusing lens to bring the object into focus in accordance with the focus state detected by the focus detecting device; and a controller which varies the beam diameter via the beam-diameter varying device in accordance with a lens position of the focusing lens which is detected via the autofocus drive system.
In an embodiment, the controller controls the beam-diameter varying device to increase the beam diameter when the object is in a predetermined short distance range.
In an embodiment, the electronic distance meter further includes a light-emitting element which emits the measuring light; wherein the beam-diameter varying device includes a lens, the beam-diameter varying device inserting and retracting the lens into and from an optical path of the light-transmitting optical system in front of the light-emitting element in accordance with the distance.
In an embodiment, the lens includes a negative lens, the beam-diameter varying device inserting the negative lens into the optical path when the object is in a predetermined short distance range, the beam-diameter varying device retracting the negative lens from the optical path when the object is in a predetermined long distance range.
In an embodiment, the lens includes a positive lens, the beam-diameter varying device inserting the positive lens into the optical path when the object is in a predetermined longer distance range, the beam-diameter varying device retracting the positive lens from the optical path when the object is in a predetermined shorter distance range.
In an embodiment, the electronic distance meter further includes a light-emitting element which emits the measuring light, wherein the beam-diameter varying device includes a moving device for moving the light-emitting element in a direction of an optical axis of the light-transmitting optical system.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-135561 (filed on May 9, 2000) which is expressly incorporated herein by reference in its entirety.